International Research Journal of Engineering and Technology (IRJET)
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EFFECT OF HEAT TREATMENT ON MECHANICAL PROPERTIES OF
ALUMINIUM 7075 ALLOY REINFORCED WITH SILICON CARBIDE AND
ALUMINA
Dattatri1, Dr. K Mohamed Kaleemulla2
of Mechanical Engineering, UBDTCE, Davangere, Karnataka, India
Professor, Dept. of Mechanical Engineering, UBDTCE, Davangere, Karnataka, India
---------------------------------------------------------------------***--------------------------------------------------------------------2Assistant
1Dept.
Abstract - In the present study, prepared specimens were
heat treated temperature to 4700C , soaking them at this
temperature for 3 hours and then furnace cooled .and
another set of samples were heat treated by temperature to
4650C , soaking them at this temp for 2 hours and then
quenched at different medium (oil, water)in order to
investigate mechanical properties. The change in mechanical
behaviour as compared to untreated samples is investigated
in terms of change in impact strength and hardness. Result
showed that the mechanical properties of aluminium metal
matrix composite by Al7075 alloy reinforced with SiC and
Al2O3 can be improved by customized heat treatment for
specific application.
Key Words: Mechanical Properties, Impact Strength,
Hardness, Metal Matrix Composite, Heat Treatment, Etc.
1.INTRODUCTION ( Size 11 , cambria font)
For the last few years, it has been discovered that the
utilization of aluminium mixtures has been increased rapidly
in different areas due to less weight, density, better
mechanical properties. Aluminium mixtures and aluminium
related matrix metal hybrid composite can be adopted in the
fabrication of different vehicle parts and aerospace
industries. Alloys are materials having metallic properties
and are made of two or more elements, at least one of which
is a metal. In the case of Aluminium alloys, most of them
contain 90 to 96% Aluminium. Aluminium alloys are
categorized under two headings i.e. wrought alloys and cast
alloys. Aluminium casting alloys are used in a large number
of applications including automobiles, trucks, transmission
of electricity, development of transportation infrastructures,
and in the aerospace and defence industries. The fast growth
of aluminium alloys in industrial applications is related to
their high strength-to-weight ratio which improves the
mechanical properties and performance of the products.
Among different foundry alloys, aluminium casting alloys are
very popular, as they have the highest cast-ability ratings,
possess good fluidity and comparably low melting points.
Their light weight and high strength-to-weight ratio are the
main reasons why cast iron and steel components are being
increasingly replaced by aluminium alloys, particularly in
the automotive industry. Choosing one casting alloy over
another tends to be determined by the relative ability of the
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alloy to meet one or more of the characteristics required for
a specific application. Heat treatment is is an important
operation in the fabrication process of any engineering
component. The objective of heat treatment is to make the
metal better suited, structurally and physically, for some
specific application. The optimum properties of aluminium
of aluminium are achieved by alloying elements and heat
treatments. This promotes the formation of small hard
precipitates which interfere with the motion of dislocation
and improve mechanical properties. One of the most
commonly used aluminium alloy for structural application is
Al7075 alloy due to its attractive comprehensive properties
such as low density, high strength, ductility, toughness and
resistance to fatigue . It has been extensively utilized in
aircraft structural parts and others highly stressed structural
application. The objective of the work are to investigate the
effects of annealing and age hardening heat treatment of
impact strength, hardness and microstructure of aluminium
7075 alloy reinforced with silicon carbide and aluminium
oxide.
2. Literature Review
Sedat ozden et al.,[1] examined the impact properties of
aluminium alloys reinforced with silicon carbide particles.
The charpy test was conducted for the specimens with
varying the temperatures from -1760C to 3000C for various
aluminium alloys 2124, 5083 and 6063 reinforced with
silicon carbide particles. Two SiC sizes of 157µm and 511µm
and two extrusion ratio of 13:63:1 and 19:63:1 were
selected. The effect strength decreases with presence of SiC
particles. SiC reinforced Al-6063 alloy shows highest impact
strength. The SEM images shows that uniform distribution of
silicon carbide particles. From this research paper we
conclude that, various base Aluminium alloy could be chosen
for the enhancement of mechanical properties.
Dr. Jassim Mohammed [2] examine the impact of warmth
treatment on mechanical properties of aluminium 2024 by
influencing the various factors like aging time, solution
treatment temperature and aging temperature. The solution
temperature was done at 5250C to 5750C (250C interval). The
ageing time also varied from 3hr to 21hr (at 6hr interval).
The aging temperature also varied from 1600C to 1900C
(150C interval). The hardness and impact toughness
increases at solution temperature 525 to 550 and minimizes
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at 575. After enhancing the aging time 3hr - 21hr at aging
temperature 1750C the hardness increases and impact
toughness decreases. This research paper concluded that
with proper solution temperature, aging temperature and
aging time the mechanical properties can be improved.
O.K Abubakre et al., [3] evaluate the mechanical properties
of aluminium 6061 which was fabricated and quenched in
various liquids like water, palm oil and sheanut oil at
elevated temperatures of 4000C, 4500C, 5300C. Various tests
like tensile, hardness and impact strength test was
conducted for quenched specimens. The result shows that
the specimen which is quenched in water at 5300C has
highest tensile strength of 109 N/mm2, yield strength of
70.89 N/mm2 and hardness of 35.50 HRC. The specimen
which is quenched in sheanut oil at 5300C shows highest
impact strength and least influence strength was detected in
water quenched specimen at 4000C. The microstructure
analysis shows that water quenched specimen at 5300C has
fine microstructure and maximum extraction of heat. From
this journal paper we came to know that, Al 6061 alloy
quenched in various liquid after heat treatment enhances the
mechanical properties.
Adeyemi Dayo Isadare et al.,[4] examined the properties of
age hardening and annealing heat treatment on the
mechanical properties and microstructural analysis of Al7075 alloy. The specimens prepared as the cylindrical rods.
Many tests like tensile, hardness and impact strength was
accompanied. The specimens were as cast (steadily cooled),
as cast (quickly cooled), annealing and age hardening. The
result shows yield strength, hardness and tensile strength,
increases in as cast (gradually cooled) specimens. Annealing
specimen shows increases in impact strength. The
microstructure shows MnZn2 microsegregations in graduall
cooling specimen. From this research paper it is reasoned
that appropriate heat treatment and rapid cooling the
microsegregation can be diminished.
3. Experimental Procedure
3.1 Material selection
 Aluminium-7075 base metal
 Silicon Carbide(SiC) and Alumina(Al2O3)
a) Base Alloy
Aluminium-7075
The aluminium alloy Al-7075 has been selected as
the matrix material is more compatible with the
reinforcement and has good mechanical property and
castability at the alloy level itself. The application of the alloy
in automobile and aircraft application itself indicated that it
is the proper selection. The material is also having good
response to age hardening, heat treatment process and
precipitation hardening. Aluminium7075 is an aluminium
alloy in which zinc is a primary alloying element.
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The composition and properties of aluminium7075
is shown below.
Table 1: composition of Aluminium-7075
Table 2: Properties of Aluminium 7075
b) Reinforcement materials
Silicon Carbide (SiC)
Silicon carbide is the only chemical compound of carbon and
silicon. It was originally produced by a high temperature
electro-chemical reaction of sand and carbon. Silicon carbide
is an excellent abrasive and has been produced and made
into grinding wheels and other abrasive products for over
one hundred years. SiC are application such as sandblasting
injectors, automotive water pump seals, bearings, pump
components extrusion dies that use high hardness, abrasion
resistance, and corrosion resistance of carbide of siicon.
Today the material has been developed into a high quality
technical grade ceramic with very good mechanical
properties.
Alumina(Al2O3)
The chemical formula of aluminium oxide is Al2O3. It is
commonly referred to as alumina, or corundum in its
crystalline form, as well as many other names, reflecting its
widespread occurrence in nature and industry. Aluminium
oxide having strong ionic inter atomic bonding gives
increase in its desirable material properties. Its most
significant use is in the production of aluminium metal,
although it is also used as an abrasive due to its hardness
and as a refractory material due to its high melting point.
Application include electrical insulator, seal faces, valve seats
etc.
Fig 1: Silicon Carbide
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Fig 2: Alumina (Al2O3)
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Table 4: Specimen composition for varying volume
fraction
Sl
AlSiC
Al2O3
no
7075
1
100%
0
0
2
90%
5%
5%
3
80%
10%
10%
4
70%
15%
15%
3.2 Stir Casting Process
Base alloy Aluminium 7075 and Reinforcement
particle SiC and Al2O3 was successfully fabricated by using
liquid vortex method. Crucible and mould box is kept for
preheating to eliminate moisture and other particles from
the inner surface. The various volume fraction of
reinforcement particles are 5%, 10%, 15% of SiC and Al2O3.
The different weight % of (SiC and Al2O3) are taken
separately in small crucibles and kept for preheat in a muffle
furnace. The preheat the reinforcement temperature was
held at 800˚C. 340 grams of Aluminium pieces is fed into the
crucible which starts melting as the temperature of open
hearth go to around 720˚C. As the temperature of furnace
reaches to 700˚C, Aluminium pieces in the crucible will melt
down. Hexachloroethane (C2Cl6) Degasifier is added to semisolid phase Aluminium, to remove the hydrogen content
from molten Aluminium. Slag formed in the crucible is
removed and preheated (800˚C) SiC and Al2O3 powder is
poured slowly into the crucible containing Liquid stage
Aluminium. Stirring action has performed with an
mechanical stirrer continuously for 5 minutes. The Cover
flux (45%NaCl+45%KCl+10%NaF) is added to the liquid
molten metal. forms a protective layer over the liquid metal
which reduces oxidation. Then liquid Aluminium poured in
to the mould box and specimen is obtained. The casted
specimens are sent for machining to perform various tests as
per ASTM standards.
3.3 Heat Treatment
There are five basic heat treatment process
i.
1Annealing
ii.
1Normalising
iii.
1Hardening
iv.
1Tempering
v.
1Case hardening
Annealing: Strengthening is heat treatment technique which
modifies the microstructure of a material to change its
mechanical or electrical properties. Heat specimen at
temperature 4700C. hold them at 3 hours in furnace 470 0C
.After that Allow to cool slowly, use a dry cooling material
(sand) or furnace Reduces internal residual stress.
Hardening: A strategy where one segment is exposed to two
full solidifying exercises or initial, a strengthening technique
joined by a solidifying strategy. Treating is a procedure of
low temperature heat treatment that is typically performed
after the solidifying procedure to accomplish the ideal
hardness/durability proportion. Process used to increase the
hardness of metal, Heat specimen at temperature 465 0C,
Holding time 2 hours maintain temp 4650C, After that
rapidly quench in cold water, oil, molten salt for few
minutes.
Tempering: Treating is a low temperature heat treatment
process regularly performed subsequent to solidifying
process so as to achieve wanted hardness/strength
proportion. After hardening process again heat specimen in
muffle furnace at temp 1200C,Holding time 5 hours maintain
temp 1200c take out the specimen form furnace and cooled
in air, it increases ductility.
Fig. 5: Heat treatment cycle.
Fig 3-Stir Casting set up
Fig 4- Casted specimen
Fig 6: Muffle Furnace
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Fig 7: specimens placed
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ii) Hardness Test
Hardness is the property of a material that enables it to
resist plastic deformation, penetration, indentation, and
scratching. The application of hardness testing enables to
evaluate material properties, such as strength, ductility and
wear resistance. The heat treated specimens were subjected
to the Vickers hardness test. The specimens were polished to
200, 400, 600, 800 and 1000 grit size of emery paper and
mounted on the machine using dwell time of 10 sec.
a) Oil quenched specimens b) Water quenched specimens
vvvvvvvvvvc) Specimen cooled in atmospheric air
Fig. 8: Specimens quenched in different media.
3.4 Test to be performed
Fig 12: Hardness Test Specimens and dimension
(ASTM E18)
i) Impact test
Impact tests are performed to assess the shock absorbing
capacity of the material under impact or sudden load. The
stresses produced in the components during impact loading
are many times more than gradual loading. Therefore impact
strength of a material is defined as the ability of a material to
withstand impact or sudden load pr unit cross sectional area.
Impact test are conducted with two types of specimen

Charpy test specimen

Izod test specimen
For this research work charpy impact test was used. The
impact load is applied to the center and behind the notch.
The specimen has standerd v-notch with included angle of
450 size of specimen according to ASTM E23for charpy
test(55*10*10).
Fig 13: Vickers Hardness Testing Machine and
prepared specimens
Testing machine consists of square pyramid indenter having
a 1360 Cone angle. Hardness test specimen has to be place in
anvil and fixed to the indenter by means of elevating screw
using hand wheel. 30 kg of load has to be applied on the
specimen at a 10 sec dwell time. Load has to withdrawn after
the dwell time. Vickers Hardness Number of a material can
be calculated using the formula
VHN = 1.854 ×
Fig 9: Impact Test Specimens after Testing
P -Applied Load
d –Indentation Diagonal measurement
iii) Microstructure Analysis
Fig 10: Impact Testing Machine Fig 11: Impact Test
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzxxxxxxSpecimens after
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxTesting
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Various mechanical properties like hardness, strength,
toughness, etc strongly influence the microstructure of the
materials. Microstructure analysis is widely used in the
industries for quality control of the materials. Optical
microscope is used to investigate the Microstructure
analysis. All specimens with various weight % of Silicon
carbide and alumina subjected for micro structural
investigation. The specimens were made good mirror
polished using 100, 220, 400, 600, 1000 grit emery paper
sequentially. The specimens were kept on the moving table
of computerized microscope and investigated at 10X, 40X,
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60X magnification. The micro images obtained are stored in
computer.
Fig 14: Computerized optical microscope and polished
specimen
4. Result and Discussion
figure shows the Impact strength value of various heat
treatments such as Air cooling, furnace cooling, water
quenching and oil quenching processes of aluminium 7075
alloy reinforced with silicon carbide and alumina is shown in
above table. It is observed that furnace cooling has lower
value of energy absorption when compared to air cooling in
the case annealing and also it is observed that furnace
cooling during annealing has lower value of energy
absorption when compared age hardening. When compared
to all heat treatment processes the air cooling has higher
value of energy absorption during annealing. Hence from the
above result we can say that the impact strength of the AMCs
is more at 10% of reinforcement for Air cooling.
ii)Hardness Test
i) Impact test (Charpy v-notch test).
Vickers hardness test
The Impact test has been conducted by using
pendulum impact testing machine as per ASTM E23 for 4
different composition of AL7075, considering aluminium as
base alloy and silicon carbide as reinforcement (SiC and
Al2O3). Totally 35 composite fabricated specimen are tested
and results are chosen for one of better values among 2or 3
trials and reading are tabulated below.
Table 5: comparison of Untreated, Air cooling,
Furnace cooling, Water quenching and oil quenching
with different composition
The heat treated samples were conducted Vickers
hardness test. The specimens were polished to 1000 microns
and mounted on the machine using dwell time 10 seconds.
P -Applied Load, d–Indentation Diagonal measurement
Table 6: Comparison of hardness values for different
heat treatment process
Fig. 15: comparison of Untreated, Air cooling, Furnace
cooling, Water quenching and oil quenching
The fabricate specimens as per ASTM (E23)
standards were tested in pendulum impact tresting machine,
the obtained values of impact strength corresponding
different composition are shown in line graph. The above
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Fig 16: Comparison of Hardness for different heat
treatment process.
The fabricate specimens as per ASTM (E18)
standards were tested in Vickers hardness testing machine,
the obtained values of impact strength corresponding
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different composition are shown in line graph. The above
figure shows the hardness values of different heat
treatments such as Air cooling, furnace cooling, water
quenching and oil quenching processes of aluminium 7075
alloy reinforced with silicon carbide and alumina is shown in
above table. It is observed that the lowest hardness values
are found for furnace cooling in te case of annealing and also
observed that the hardness values are higher for the case of
aging. Hence from the above result we can say that the
hardness of the AMCs is more at 10% of reinforcement for
the case aging.
iii) Microstructure Analysis
Microstructure of the composite samples reveals the
presence and homogenous distribution of reinforcements in
the Al 7075 matrix. Microstructure examination was
conducted by optical microscope. The microstructure of the
material can strongly influence physical properties like
strength, ductility, hardness, toughness, corrosion resistance
and wear resistance. microstructure of a prepared surface
specimen tested by inverted metallurgical microscope of
10X, 40X, 60x and 100X magnification. The formation of
dendritic structure resulted by solidification process
observed before heat treatment of composite Metallographic
examination were carried out to see the distribution of silico
carbide and alumina particulates in aluminum metal matrix
and investigates the condition of grains both as cast and
heat-treated composite metal matrix as shown. Silicon
carbide and alumina particles melted and mixed
homogenously by heat treatment and uniform distribution of
reinforcements.
Fig.19: Microstructure of untreated 7075 Al alloy
reinforced with SiC and Al2O3
5. Conclusions
The study on the effect of various heat treatment
processes on Aluminium 7075 alloy reinforced with silicon
carbide and alumina was conducted and attempt were made
to relate mechanical properties such as hardness, Impact
strength and also study on Microstructure after heat
treatment. The following conclusion was made regarding the
effect of various heat treatment processes.
1.
2.
3.
4.
5.
Aluminium alloy hybrid composite has been
fabricated using stir casting technique. Stir casting
technique is the most economical and conventional
method of casting composites.
It has been found that rapid solidification process
and heat treatment eliminate formation of micro
segregation and significantly improved some
mechanical properties.
Annealing heat treatment operation improves
impact strength but lower hardness values.
The hardness values are higher for the case for the
case of aging in oil quenching.
The lowest hardness values are found for the case of
furnace cooling.
Scope of Future Work
Fig. 17: Microstructure of Age hardening 7075 Al alloy
reinforced with SiC and Al2O3.
1.
2.
The research work is extended further by varying
temperature of various heat treatment process
The other reinforcement such as boron carbide,
titanium carbide, graphite etc can also be used with
aluminium alloys in order to enhance its property
and use it for different application.
Fig. 18: Microstructure of annealed 7075 Al alloy
reinforced with SiC and Al2O3.
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